The present invention relates to a piston ring for use in an internal combustion engine, and more particularly, to a type thereof in which improvement is made on a sliding characteristic at an initial operation stage of the engine.
In accordance with a recent demand in light weight and high output engine, high quality is required in the piston ring. In this respect, conventionally, a sliding surface of the piston ring has undergone several treatment so as to impart wear resistance thereon in order to prolong durability or service life thereof. For example, high hardness chromium plating layer or sprayed layer is provided on the sliding surface of the piston ring. Alternatively, nitriding treatment is effected to the sliding surface.
Among these treatments, the nitriding treatment provides superior wear resistivity, and therefore, the piston ring having nitriding layer have been widely used under a severe working or operating conditions.
However, even though the nitriding layer has excellent wear resistivity, the layer would be insufficient in view of thermal seizure or scuffing resistivity in comparison with the high hardness chromium plating or sprayed layer. Accordingly, further improvement must be made on the piston ring having the nitriding layer in an aspect of abnormal wearing or scuffing occurred under the severe engine working condition.